Sediment trapping efficiency and grain size distribution: Influence of cascading check dam systems on the debris flow movement process

Debris flow disasters frequently occur worldwide and cause huge losses. Check dams are one of the most effective geotechnical engineering measures to mitigate debris flow hazards. However, the effects on sediment trapping efficiency and particle sorting function are unclear due to the design parameters of cascading check dams, such as dam location, number, and spacing. This limits the overall ability of cascading dam systems to effectively intercept sediment and regulate grain size distributions. In this study, flume experiments were conducted to investigate the sediment trapping efficiency of four cascading dam systems comprising closed- and open-type check dams, and then to analyse the grain size distribution characteristics of sediment deposited in dam reservoirs. The results indicated that the total trapping efficiency of the cascading check dam system ranges from 45% to 85%, and the grain size distribution parameter ( μ , indicating fine-particle content) decreases as the number of open-type dams increases. Due to differences in interception role of cascading dam combinations, upstream open-type dam trap more coarse particles and discharge finer particles into the downstream, while the downstream closed-type dams intercept both coarse and fine particles. Therefore, designing cascading dam systems with progressively smaller openings downstream is recommended to trap coarse sediment in upstream reservoirs while directing fines to downstream dams. Finally, we propose and validate a suitable equation for calculating the sediment trapping ratio across different cascading dam series, demonstrating its accuracy and applicability compared to previous findings.